The subject invention relates to a beam selector for a laser and in particular, to an improvement in a medical laser photocoagulator. For quite some time, surgeons have been using the beam from a laser source to perform delicate eye surgery. One of the advantages of using a laser beam for surgery is that it can be tightly focused on the area to be treated. Another advantage is that different tissues in the eye absorb different wavelengths of light. Therefore, a beam which will pass harmlessly through the cornea can be used to treat retinal tissue at the back of the eye. In use, the doctor will select a particular wavelength radiation which will be highly absorbing in the tissue to be treated, while not causing damage to surrounding tissues.
For quite some time, gaseous ion lasers were used in medical photocoagulators. In a gaseous ion laser, a gas is energized to create an excited state of ions which emit radiation at certain specific wavelengths. Different wavelengths can be generated by using different gases. One of the most common ion lasers used for eye surgery is an argon ion laser. This type of laser produces significant output lines at 488 and 514 nanometers. In contrast, an ion laser filled with krypton gas will generate significant power at laser lines having wavelengths 531, 568, 647 and 676 nanometers. In some photocoagulators, both an argon and a krypton gas laser are used to provide a wider range of wavelength lines.
About one and a half years ago, the assignee of the subject invention, Coherent, Inc., introduced a new photocoagulator which combined an ion laser and a dye laser. In a dye laser, the laser cavity includes a fast flowing stream of fluid which is colored with an organic dye. The laser cavity is excited or pumped using another laser, such as an ion laser or an eximer laser. One of the primary advantages of a dye laser is that the output can be tuned. Thus, rather than merely producing individual lines similar to an ion laser, a dye laser is capable of generating laser radiation over a range of wavelengths. The present dye laser used in the assignees photocoagulator emits radiation across a spectrum from 577 to 630 nanometers.
In the combination ion and dye laser system, marketed as the 900 series photocoagulator by Coherent, Inc., the argon ion laser or primary laser performs two alternate functions. In one mode, the beam from the argon laser is used to pump the cavity of the dye laser. In the other mode, the argon laser beam itself is used for surgery. In this manner, the shorter wavelength argon lines are available to the surgeon.
In order to achieve this result, the optics in the photocoagulator are required to direct the argon ion laser beam along one of two paths. In one path, the argon beam is channeled directly out of the device through a fiber optic wand. The optics are also capable of directing the argon ion laser beam along a second path to pump the dye laser.
The optical alignment necessary to deliver the argon laser beam to the dye laser is critical. Accordingly, the fixed optics in the device are typically set to direct the argon ion laser beam directly to the cavity of the dye laser. The optics further include a movable member for selectively intercepting and redirecting the argon beam to the fiber optic input of the photocoagulator. Even though alignment of the beam along this second path is less critical than the alignment required to pump the dye laser, it nonetheless must be accurately controlled in order to properly deliver the laser beam to the output portion of the device.
In the prior art device described above, a mirrored reflector was mounted on a translatable car which was movable into the path of the argon ion laser beam. The car was journalled on races that included precision made ball bearings. The translatable car was difficult to fabricate and expensive. In addition, the device was relatively heavy, requiring a strong motor to actuate. It was also found to be difficult to ensure that the tracks maintained perfect alignment as the reflector was moved into and out of the path of the argon ion laser beam. Thus, it could be desirable to provide an improved beam selector which overcomes the problems found in the translatable car of the prior art.
As mentioned above, some photocoagulators have both an argon ion laser and a krypton ion laser. In these devices, only one of the two lasers is used at any particular time. A beam selection system must still be provided to insure that both laser beams will ultimately travel along the same path to the output of the device. In the prior art argon/krypton photocoagulators, this result was achieved through the use of a fixed position beam splitter or dichroic mirror which selectively passes different laser wavelength lines. The design and fabrication of such optical elements can be expensive. Furthermore, it is difficult to design a single splitter which will reflect all of the argon laser lines but transmit all of the krypton laser lines. Nonetheless, the latter approach was still preferred over the complex translatable car used in the argon/dye photocoagulator described above. However, if an improved movable selector were designed, it could be used to replace the complex and expensive optical beam splitters.
Accordingly, it is an object of the subject invention to provide a new and improved apparatus for selectively intercepting and redirecting a laser beam.
It is another object of the subject invention to provide a new and improved apparatus for accurately intercepting and redirecting a laser beam in a photocoagulator.
It is a further object of the subject invention to provide a new and improved apparatus for selectively redirecting a laser beam that is lightweight in construction and can be easily moved.
It is still another object of the subject invention to provide a new and improved apparatus for intercepting and redirecting a laser beam which is simple to manufacture yet is highly accurate.